Gas turbine engines typically include a compressor section, a combustor, and a turbine section. A rotor shaft rotatably couples the compressor section and the turbine section. In this respect, the compressor compresses air entering the gas turbine engine. This compressed air mixes with fuel in the combustor to form an air and fuel mixture, which produces hot exhaust gases when ignited. These hot exhaust gases then flow through the turbine section before exiting the gas turbine engine. The turbine section extracts kinetic energy from the exhaust gases, which, in turn, rotates the rotor shaft. The rotation of the rotor shaft provides the necessary mechanical energy to the compressor section to compress the incoming air.
In order to start the gas turbine engine, it is necessary to rotate the rotor shaft to provide compressed air to the combustor. But, the turbine section is unable to rotate this shaft during starting because the combustor is not yet producing exhaust gases. In this respect, a starter (e.g., an electric motor, hydraulic motor, pneumatic motor, etc.) must rotate the rotor shaft until the combustor produces exhaust gases.
Typically, the starter indirectly couples to the rotor shaft in conventional gas turbine stating systems. More specifically, the starter rotates an axial shaft, which couples to a transfer gearbox (TGB). The TGB transfers the rotation of the axial shaft to a radial shaft. That is, the TGB converts the axial rotation into radial rotation. An inlet gearbox (IGB) or a power takeoff (PTO) transfers the rotation of the radial shaft to the rotor shaft. That is, the IGB/PTO converts the radial rotation back to axial rotation.
But, the TGB, IGB/PTO, radial shaft, and axial shaft are expensive and time consuming to manufacture and assemble. Furthermore, these components increase the overall complexity and weight of the gas turbine engine. Accordingly, a starting system for a gas turbine engine that couples the starter directly to the rotor shaft without the need for multiple gearboxes and/or additional shafts would be welcomed in the technology.